Ballpoint assembly



y 14, 1970 M. B. GORDON ET AL 3,520,630

BALLPOINT ASSEMBLY Filed March 1, 1968 MAURIECE BEVERLY GORDON ANDSANFORD D. HElL INVENTORS.

BY PAUL E. SULLIVAN,

ATTORNEY United States Patent US. Cl. 401-=-215 2 Claims ABSTRACT OF THEDISCLOSURE This application illustrates and describes a ball typedispensing assembly. There is provided a reservoir for a marking mediumsuch as a liquid ink, cosmetic, or the like, and a dispensing assemblyextending from one end of the reservoir. This assembly includes a rigidtip having a ball socket communicating with the reservoir through aconduit, and a ball rotatably housed within the socket for transferringthe marking medium onto a surface as it rolls thereover. At least theouter or contact surface of the ball is composed of a multiplicity ofrandomly and compactly disposed crystals of aluminum oxide of an averagediameter ranging up to about microns, the crystals being sinteredtogether to form a dense, substantially non-porous structure which issignificantly stronger than a single crystal aluminum oxide ball, yetsubstantially less expensive,

BACKGROUND OF THE INVENTION Field of the invention The present inventionis directed to an implement for applying a marking medium and moreparticularly to an improved dispensing assembly of the revolving balltype.

Description of the prior art In the usual ballpoint pen, proper anduniform deposit of ink throughout the life of the implement depends uponcertain basic requirements that are directly associated with the writingassembly and particularly the surface characteristics of the ball. Forinstance, the surface of the ball should be sufiiciently wettable toinsure that a thin but continuous and uniform film of ink is present asthe ball rolls into contact with the writing surface. There must besufliciently greater paper-ball friction than ballsocket friction toinsure that the ball will rotate evenly and continuously during use ofthe pen. Also, the ball should be inert to the ink and non-reactive withthe tip in the presence of ink to prevent any detrimental chemical orelctro-chernical change in the system. Further, a minimum of wear shouldoccur in the socket as a result of sliding engagement with the ball.

For the first few years after ballpoint writing pens were introduced inthe mid 1940s, a polished carbon steel or stainless steel ball wasemployed in the usual pen. And while such balls performed reasonablywell under optimum conditions, certain problems quickly became evidentin their use. In some instances, their polished surfaces were notsufficiently wettable by the ink to assure an even unbroken film, andeven more significantly they had a tendency to slide or skip on glazed,slick 'or greasy surfaces. Also, problems were encountered as a resultof corrosion of the ball by the ink, as well as galvanic action betweenthe ball and tip in the presence of the ink.

As a result of the ballpoint industrys early recognition of thesevarious problems, a substantial amount of research work has been done onwriting assemblies and particularly on the balls in an effort to providea permanent ball surface which will not react with the ink or 3,520,630Patented July 14, 1970 tip and which will carry a uniform coating of inkwhile providing sufficient friction with the paper to assure continuousrotation. As one possible solution for some of these problems, it hasbeen suggested that the surface of a steel ball be mechanically,chemically or electrolytically converted to a slightly roughened orstain finish. And while such converted balls initially appear to havereasonably good ink carrying capabilities and writing characteristics,such improvements generally are of a transient nature as the satinfinish is gradually destroyed by the polishing action of the paper onwhich it is used. Thus, after extended use, such balls may lose much oftheir ink carrying and paper gripping capabilities resulting in acondition commonly referred to as skipping. Further, in some intancessuch satin finishes have caused excessive wear of the ball supportingsurfaces within the tip socket, thus resulting in undersirable ballrecession with attendant problems of excessive ink flow, gooping andgeneral messiness.

At a relatively early stage of this work by the industry, it was foundthat very good performance characteristics were obtained with a writingasembly containing a ball ground from a synthetic ruby or sapphireblanka single aluminum oxide crystal containing a trace amount of animpurity such as chromium or iron. Such a ball was not only found to beinert to and readily wettable by ballpoint inks, but to give a minimumof socket wear while still writing well on slick and/or greasy surfacesthat would cause a standard steel ball to skip badly.

Unfortunately, single crystal aluminum oxide ball have not proven to becommercially practicable except in a few high cost, low volume pens. Notonly do they cost anywhere from about six to twenty times more thanother balls, but even more importantly, they are extremely difiicult toassemble into tips on a practical basis with modern high volumeproduction equipment. Being of a single crystal, the balls appear tohave natural areas or planes of weakness which extend from surface tosurface and which cause a relatively high percentage of cracking andbreaking as a result of stresses generated therein during the ballinsertion, seating and lip spinning operations. Thus, aside from theinitial expense of such balls, production costs are very high because ofexcessive losses in scrapping broken balls and inoperative tips. As aresult, the use of the single crystal aluminum oxide balls has not beeneconomically or practically feasible for medium and low priced ballpointpens.

The above mentioned cracking problem can be alleviated somewhat byreducing the amount of seating and spinning pressures and consequentclosure of the lip. However, such a solution generally is notcommercially acceptable because of the objectionable wet or heavy inkdeposit product by a tip closed in this manner.

SUMMARY OF THE INVENTION The present invention not only provides all ofthe desirable characteristics and advantages of a ballpoint writingassembly containing a ruby or sapphire ball but improves upon them inmany instances, while eliminating the serious cost and productionproblems previously inherent with such a ball. These surprising resultsand advantages were discovered to be provided by use of a writingassembly containing a ball having a surface which is composed ofaluminum oxide base ceramic, such ceramic being characterized by amultiplicity of randomly oriented, minute aluminum oxide (corundum)crystals that are sintered together to form a strong, dense compact masshaving little or no porosity.

This random orientation of small particles provides a structure in whichthere appears to exist no continuous surface to surface planes or areasof fracture, whereby its integrity will not be affected unless it issubjected to sub- 3 stantially greater force than that required to breaka single crystal ball. Thus, a multicrystalline aluminum oxide ball ofthe type used in the present invention is sufficiently durable and crackresistant to permit its processing and assembly into writing tips inpresent day high volume production and assembly equipment.

In addition to its crack resistance, the present multicrystal ball isinert, it exhibits no galvanic action with a metallic tip in thepresence of ink, it has good afiinity for ink thereby not requiringroughening, it is highly resistant to wear, and it has the same smoothwriting characteristics as, while being less expensive than, the singlecrystal aluminum oxide ball proposed heretofore. Even including theexpense of forming ball blanks from and sintering the small particles orcrystals, the present multicrystal ball can be made at a cost of lessthan 50 percent of that of prior single crystal balls.

Therefore, a principal object of this invention is the provision of aballpoint assembly containing a non-metallic, crack resistant ballhaving a contact surface formed of a multiplicity of randomly orientedaluminum oxide crystals sintered together into a dense mass.

Yet another object of this invention is to provide a writing tipcontaining a writing ball composed of a multiplicity of minute crystalsof an aluminum oxide, such crystals being randomly oriented and sinteredtogether to form a dense, substantially non-porous mass which is highlyresistant to cracking and wear.

A still further object of this invention is the provision of a writingtip containing a synthetic ball formed of aluminum oxide and having ahard, non-porous surface which is relatively smooth yet readily wettableby ballpoint inks, and an internal structure which is highly resistantto cracking under stresses normally encountered in ballpoint tipmanufacturing and assembly operations.

Yet another object of this invention is to provide an improved writingassembly containing a crack resistant writing ball formed of aluminumoxide and which is substantially lower in cost than previously proposedruby or sapphire writing balls.

Further and additional objects and advantages of this invention will beapparent from the following description when taken in conjunction withthe appended drawing, in which:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal sectionalview of a ballpoint assembly embodying the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1,there is illustrated a ballpoint assembly 10, which includes asubstantially rigid tip 12 formed of a suitable material and providedwith a ball socket 14 and an ink conduit 16 extending between the socketand the vented reservoir 18 on which the assembly is mounted. As will beunderstood by those in the art, the tip may be fabricated or otherwiseformed of a metal such as stainless steel or bronze, or a syntheticpolymeric resin of which polycarbonate, polytetrafiuoro ethylene, orpolyacetal are a few examples.

Housed within the socket 14 for universal rotation therein is a writingball 20 which is composed of aluminum oxide base ceramic characterizedthroughout by a multiplicity of minute crystalline particles of aluminumoxide, the particles being sintered together to form a dense mass havingrelatively little or no porosity.

The crystalline particles are disposed throughout the ball in anon-oriented or random manner. And even though each of the smallindividual crystalline particles may have one or more natural areas ofweakness, as with a larger single crystal, it will be obvious that theseareas are not oriented or connected. As a result, the ball 20 has nosingle fracture planes extending from one surface to another, as in asingle crystal ball. The improvement in crack resistance in the presentball is very graphically illustrated by a simple comparison between thebreak resistance of a group of the present balls with that of a group ofsingle crystal balls. As indicated by the following table, the presentballs were found to withstand an average of about 200 pounds of directloading before breakage, as compared with an average of about 92 poundsfor a group of single crystal balls.

TABLE I Pounds of direct loading required for ball breakage Singlecrystal Multicrystal ruby aluminum oxide 215 250 127 249' 120 206 101198 91 193 191 7 1 189 53 184 43 174 25' 164 High 215 High 250 Mean 92Mean 200 Low 25 Low 164 The tests represented by above Table I were madeon an Instron TM instrument, a testing machine commonly used inlaboratories for compression and tensile strength testing. For thisseries of tests, the Instron was fitted with a standard 0-1000 lb. CDcompression cell, and a steel plate having a shallow concave depressionfor positioning the ball properly relative to the compression cell.

The density of the fired ball should preferably be at least about 3.4grams per cubic centimeter and the aluminum oxide crystals shouldpreferably fall within an average range size not greater than about 20microns in diameter, although they may go'up to about 30 microns withsatisfactory results. Particularly for balls having a diameter of lessthan about 1 mm., after polishing, by far the best results have beenobtained with a fired ball blank having a density above 3.8 grams percubic centimeter and an average aluminum oxide crystal size of less than10 microns. The high density and small crystal size are apparentlysignificant in the attainment of the desired smooth surface in thepolishing operation.

In the above discussion of crystal size, it will be understood that theranges given are not absolute but rather constitute an average of thecrystals, and that a percentage of the crystals in any given range maybe larger than the average. Also, it will be understood that in thecontext of this application, the term diameter is used broadly toinclude the size of a crystal in its largest dimension.

Alumina base ceramic contains upwards of about by weight aluminum oxidean the remainder small amounts of mineralizers or glass forming oxideswhich can be added as silica, the silicates such as clay and talc, thealkali and alkaline earth oxides, carbonates, phosphates and the likesuch as the oxides, phosphates or carbonates of sodium, calcium,strontium and magnesium; and various other of the metal oxides such aschromium oxide, manganese oxide and the like known in the art for theirglass modifying or grain growth inhibiting effect when used in smallamounts in high alumina ceramics. Examples of specific sintered aluminumoxide base ceramics are as follows, the percentages in each case beingby weight: aluminum oxide; 99.5% aluminum oxide, .5 chromium oxide; 94%aluminum oxide, 4% silica, 2% calcium oxide; 85% aluminum oxide; 10%silica, 5% calcium oxide. In all of these examples where silica ispresent in the raw batch, either as such or in a combined form, thefinal ceramic structure after the tity of sand, with the writing ormarking assembly being mounted on the wagon and movable between aposition spaced from the writing surface and a position contacting thesurface under a predetermined load. For each unit, the coeflicient offriction was determined to be the difference in the weight of sandrequired to move the wagon when the unit was in each of the twopositions.

This reduced friction manifests itself in a much smoother and morecontrollable writing feel, which difference is subjectively evident tomost users.

It is to be understood that the foregoing description and accompanyingdrawings have been given only by way of example and illustration. Forinstance, the ball may be used in dispensing units for fluids other thanballpoint writing ink. Accordingly, this invention is to be consideredas limited only by the following claims.

We claim:

1. A ballpoint assembly including a substantially rigid tip defining aball receiving socket and a fluid conduit opening into said socket; anda smooth surfaced ball housed within said socket for universal rotationtherein, said ball consisting of sintered aluminum oxide base ceramichaving a density of at least 3.4 grams per cubic centimeter andcontaining at least 85% by weight aluminum oxide present in the form ofrandomly oriented crystals having an average size not exceeding 20microns.

2. A ballpoint assembly as set forth in claim 1 wherein said aluminumoxide base ceramic has a density of at least 3.8 grams per cubiccentimeter and wherein the average size of the aluminum oxide crystalsdoes not exceed 10 microns.

References Cited UNITED STATES PATENTS 2,396,058 3/1946 Rath 401-1983,094,103 6/1963 Trefzer 401-215 3,166,618 1/1965 Fehling et a1. 401-216X 3,303,825 2/1967 Shuman et al 40121S FOREIGN PATENTS 622,959 5/ 1949Great Britain.

691,469 5/ 1953 Great Britain.

818,317 12/1951 Germany.

250,923 12/ 1947 Switzerland.

LAWRENCE CHARLES, Primary Examiner US. Cl. X.R. 401-216

